1. Field of the Invention
The present invention relates to a vertical CVD (Chemical Vapor Deposition) apparatus and a CVD method using the same, for a semiconductor processing system. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an LCD (Liquid crystal display) or FPD (Flat Panel Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In order to manufacture semiconductor devices, CVD 20 processes and pattern etching processes are repeatedly applied to a semiconductor wafer. As semiconductor devices are becoming more and more highly miniaturized and integrated, demands on CVD processes have become stricter. For example, very thin insulating films, such as capacitor insulating films and gate insulating films are still required to be thinner and to be more insulating.
In relation to CVD processes, a so-called ALD (Atomic Layer Deposition) is known as a technique for improving the quality of a film to be formed. ALD is performed by alternately supplying at least two reactive gases pulsewise to repeat two steps, i.e., a step of causing one of the reactive gases to be adsorbed on a wafer, and a step of causing the other of the reactive gases to act on the adsorbed reactive gas. As a consequence, thin layers formed by respective step-cycles are stacked, thereby forming a film having a predetermined thickness.
In the process of manufacturing semiconductor devices, a semiconductor processing apparatuses is used for performing a process on a target substrate, such as a semiconductor wafer. A vertical heat-processing apparatus for simultaneously heat-processing a number of wafers is known as a processing apparatus of this kind. In general, a vertical heat-processing apparatus includes an airtight vertical process chamber (reaction tube) configured to accommodate wafers. A load port is formed at the bottom of the process chamber and is selectively opened and closed by a lid, which is moved up and down by an elevator.
In the process chamber, the wafers are stacked at intervals in a holder called a wafer boat, while they are placed in a horizontal state. The wafer boat with the wafers held thereon is placed on the lid, and loaded and unloaded into and from the process chamber through the load port by the elevator.
U.S. Pat. No. 6,585,823 B1 discloses an example of a vertical heat-processing apparatus arranged to perform a CVD process of the ALD type. The apparatus disclosed in this publication includes a process chamber having a double tube structure, which is formed of an inner tube and an outer tube. Two reactive gases are alternately supplied from the bottom of the inner tube, and pass through gaps between the stacked wafers, and then flow into an exhaust passage from the top of the inner tube.
Jpn. Pat. Appln. KOKAI Publication Nos. 2003-45864 and 2003-297818 disclose other examples of a vertical heat-processing apparatus arranged to perform a CVD process of the ALD type. The apparatuses disclosed in these publications include a process chamber having a single tube structure, in which a buffer chamber common to two reactive gases is disposed and extends in a vertical direction. The buffer chamber is provided with delivery holes formed thereon and arrayed substantially entirely over the vertical length of stacked wafers. The two reactive gases are alternately supplied into the buffer chamber, and flows out toward wafers through the delivery holes.